There are three major changes to the Media Object modules for SMIL 3.0:
the first is the splitting of the SMIL 2.1 MediaParam module into two
modules: the MediaParam and MediaRenderAttributes modules;
the second is the introduction of the MediaOpacity module, containing new
rendering attributes for chroma key and opacity control; the third is the
introduction of the MediaPanZoom
module. The rationale for these changes is:

The splitting of the SMIL 2.1 MediaParam module provides a better
differentiation of functionality, which may help user agent profile
designers be more selective in the features they wish to support.

The MediaPanZoom module defines the panZoom attribute to provide a
framework for panning and zooming over media content. (This attribute is
based largely on equivalent functionality in the SVG viewBox
attribute.)

The MediaParam module also includes
new text that explicitly discusses the behavior of adding the various media
control attributes defined in that section to a SMIL layout region definition
as a means of providing a global mechanism for applying default attribute
settings to all content rendered within that region.

A number of editorial changes have also been integrated into the various
Media Object modules descriptions; these do not impact the functionality
defined in earlier versions of SMIL.

This section provides convenience definitions for common timing and
resource identifier terms used in this module.

SMIL provides a number of timing-related concepts that are used to
determine activation, duration and termination of media objects in a
presentation. The temporal semantics of these concepts are discussed in the
SMIL 3.0 Timing and Synchronization module.

The duration of a referenced media item based on the temporal
properties of that item (defined next), without any explicit SMIL
timing markup. Some media objects have a well-defined notion of
implicit duration (such as a 7 second audio clip), while other objects
do not have well-defined durations (such as a string of plain text). In
SMIL, the implicit duration for any media object that does not have a
well-defined duration is set to be zero seconds. The implicit duration
is used to calculate scheduling information; it is sometimes
independent of the actual duration of a media object (such as with a
live media stream or with an image with multiple internal frames when
no particular duration can be derived by the SMIL scheduler). From a
scheduling perspective, an object's intrinsic duration forms the basis
for the simple
duration of the object during presentation. This duration may be
shortened or extended using SMIL timing markup.

Media objects, such as stored audio or video files, for which there
is a measurable and well-understood duration. For example, a five
second audio clip is continuous media, because it has a well-understood
duration of five seconds. Opposite of "discrete media". See also the definition of
continuous media in the Timing module.

Media objects, such as images or non-timed text data, that has no
obvious duration. For example, a JPEG image is generally considered
discrete media, because there's nothing in the file indicating how long
the JPEG should be displayed. Opposite of "continuous media". See also
the definition of
discrete media in the Timing module.

The distinction between continuous and
discrete media is sometimes arbitrary and may be SMIL renderer dependent. For
example, animated images that do not have a well-defined duration (simply a
repeating collection of frames) are classified for SMIL scheduling purposes
as being discrete media; such objects have an intrinsic scheduling duration
of zero seconds.

In this specification, the term URI [URI] refers to a universal resource
identifier, as defined in [RFC3986] and subsequently extended under the
name IRI in [RFC3987]. In some cases, the term URI has been retained in the
specification to avoid using new names for concepts such as "Base URI" that
are defined or referenced across a whole family of XML specifications.

All of these media elements are semantically identical. When playing back
an external media object, the player must not derive the exact type of the
media object from the name of the media object element. Instead, it must rely
solely on other sources about the type, such as the type information
communicated by a server or the operating system, or by using type
information contained in the type
attribute.

This section is informative.

Authors are encouraged to use meaningful synonyms (animation, audio, img,
video, text or textstream) when referencing external media objects. This is
in order to increase the readability of the SMIL document. Some SMIL
implementations may require the use of an element type that matches the
information type of the object. When in doubt about the group of a media
object, authors should use the generic "ref" element.

The animation element defined here should not be confused with the
elements defined in the SMIL 3.0 Animation
Module. The animation element defined in this module is used to include
an external animation object file (such as a vector graphics animation) by
reference. This is in contrast to the elements defined in the Animation
module, which provide an in-line syntax for the animation of attributes and
properties of other elements.

SMIL 3.0 also supports the smilText element for defining in-line
timed text content. This functionality is described in the smilText Modules specification.

Anchors and links may be attached to visual media objects, i.e. media
objects rendered on a visual abstract rendering surface.

Attributes Definitions

Languages implementing the SMIL BasicMedia Module must define which
attributes may be attached to media object elements. In all languages
implementing the SMIL BasicMedia module, media object elements may have the
following attributes:

The value of the src attribute is the IRI [IRI] of the media element, used for locating
and fetching the associated media.

The attribute supports fragment identifiers and the '#' connector in
the IRI value. The fragment part is an id value that identifies one of
the elements within the referenced media item. With this construct,
SMIL 3.0 supports locators as currently used in HTML (that is, it uses
locators of the form http://www.example.org/some/path#anchor1),
with the difference that the values are of unique identifiers and not
the values of "name" attributes. Generally speaking, this type of
addressing implies that the target media is of a structured type that
supports the concept of id, such as HTML or XML-based languages.

Note that this attribute is not required. A media object with no
src attribute has an intrinsic
duration of zero, and participates in timing just as any other media
element. No media will be fetched by the SMIL implementation for a
media element without a src
attribute.

The type attribute
is used for purposes of content selection and when the type of
the referenced media is not otherwise available. It may be
overridden by the contents of the RTSP DESCRIBE response or by
the static RTP payload number.

The type attribute
is used as an alternative method of content selection and when
the type of the referenced media is not otherwise available. It
may override the contents of the "Content-type" field in an HTTP
exchange only if a user has allowed such overrides, as specified
in the TAG Finding Authoritative Metadata [AM]. The nominal
precedence order for type resolution is: via the HTTP
content-type field, via the type attribute, and then by using
other clues (such as file inspection or use of the file
extension).

The type attribute
value takes precedence over other possible sources of the media
type (for instance, the file extension).

When the content represented by a URL is available in many data
formats, implementations MAY use the type value to influence which of
the multiple formats is used. For instance, on a server implementing
HTTP content negotiation, the client may use the type attribute to order the
preferences in the negotiation. The type attribute is not intended
for use in media sub-stream selection.

For protocols not enumerated in this specification, implementations
should use the following rules: When the media is encapsulated in a
media file and delivered intact to the SMIL user agent via a protocol
designed for delivery as a complete file, the media type as provided by
this protocol should take precedence over the type attribute value. For
protocols which deliver the media in a media-aware fashion, such as
those delivering media in a manner using or dependent upon the specific
type of media, the application of the type attribute is not defined by
this specification.

Element Content

Languages utilizing the SMIL BasicMedia module must define the complete
set of elements which may act as children of media object elements. There are
currently no required children of a media object defined in the BasicMedia
Module, but languages utilizing the BasicMedia module may impose requirements
beyond this specification.

If the including profile supports the XMLBase functionality [XMLBase], the values of the src and longdesc attributes on the media object
elements must be interpreted in the context of the relevant XMLBase URI prefix.

User-agent implementations are responsible for defining the rendering
behavior when fragment addressing is used in the src attribute. Such definition should be added
to language profiles that wish to include specific media addressing features.
For example:
- User-agents should define the default behavior for when referencing a
non-existing id in the target media document.
- User-agents should define the rendering method for the selected media
fragment: in context, with or without highlighting and scrolling, or
stand-alone (selective rendering only).
- User-agents should describe the timing implication for when addressing
timed-content.

SMIL 3.0 allows but does not require user agents to be able to process
XPointer values in the IRI value of the src attribute. The SMIL 3.0 Linking
Module provides additional information related to XPointer.

This section defines the elements and attributes that make up the SMIL
MediaParam Module definition. The MediaParam module is intended to provide a
uniform mechanism for media object initialization. Languages implementing
elements and attributes found in the MediaParam module must implement all
elements and attributes defined below, as well as BasicMedia.

The param element allows a general
parameter value to be sent to a media object renderer as a name/value pair.
This parameter is sent to the renderer at the time that the media object is
processed by the scheduler. It is up to the media renderer to associate an
action with the given param. The media renderer may choose to ignore any
unknown or inappropriate param values (such as sending a font size to an
audio object).

Any number of param elements may
appear (in any order) in the content of a media object element or in a paramGroup element. If a given
parameter is defined multiple times, the lexically last version of that
parameter value should be used.

The syntax of names and values is assumed to be understood by the object's
implementation. The SMIL specification does not specify how user agents
should retrieve name/value pairs.

["data"|"ref"|"object"] This attribute specifies the type of the
value attribute. Possible
values:

data This is default value for the
attribute. It means that the value specified by value will be evaluated and
passed to the object's implementation as a string.

ref The value specified by value is a IRI [IRI]that designates a resource where
run-time values are stored. This allows support tools to identify
URIs given as parameters. The IRI must be passed to the object
as is, i.e., unresolved.

object The value specified by value is an identifier that refers
to a media object declaration in the same document. The identifier
must be the value of the id
attribute set for the declared media object element.

This attribute specifies the content type of the resource designated
by the value attribute
only in the case where valuetype is set to "ref". This
attribute thus specifies for the user agent, the type of values that
will be found at the IRI designated by value. See 6.7 Content
Type in [HTML4] for more
information.

Example

This section is informative.

To illustrate the use of param,
suppose that we have a facial animation plug-in that is able to accept
different moods and accessories associated with characters. These could be
defined in the following way:

4.5.2 The paramGroup element

The paramGroup element
provides a convenience mechanism for defining a collection of media
parameters that may be reused with several different media objects. If
present, the paramGroup element
must appear in the head section of the
document. The content of the paramGroup element consists of zero or
more param elements. The paramGroup element may not contain
nested paramGroup element
definitions.

Element attributes

This element does not define any new attributes. Profiles integrating this
element must specify an attribute of type ID [XML11] by which the param
group is referenced in a media object reference. For SMIL 3.0, the xml:id
attribute will typically be used.

Examples

This section is informative.

This section contains several fragments that illustrate uses of the paramGroup element.

In the following fragment, a paramGroup is created to define parameters
that are passed to several different media objects:

In this final example, a media object provides a duplicate param value.
The behavior in this case depends on the media renderer; all param values are
passed to the renderer in the lexical order of the SMIL source file. It is
expected that the lexically last value for any parameter sent to the renderer
be used, if possible.

Used to specify the name of a paramGroup that was defined in
the document head. The value is a
single IDREF [XML11] that refers to the ID [XML11] of a paramGroup element. If the named
paramGroup does not exist,
this attribute is ignored. If this attribute is defined on a SMIL
layout region definition, it specifies a default value for all content
displayed within that region.

Any profile that integrates the functionality of this module is strongly
encouraged to define a set of common parameter names that may be used to
initialize common media object types for that profile. This can significantly
increase interoperability of user agents and media rendering libraries.

The supported uses of the type
and valuetype attributes on
the param element must be specified by
the integrating profile. If a profile does not specify this, the type and valuetype attributes will be
ignored in that profile.

This section defines the elements and attributes that make up the SMIL
MediaRenderAttributes Module definition. Languages implementing elements and
attributes found in the MediaRenderAttributes module must implement all
elements and attributes defined below, as well as BasicMedia.

Controls the behavior of the media object after the effects of any
timing are complete. For example, when SMIL Timing is applied to a
media element, erase controls the display of the media when the active
duration of the element and when the freeze period defined by the fill attribute is complete (see SMIL Timing and Synchronization module). If
this attribute is defined on a SMIL layout region definition, it
specifies a default value for all content displayed within that region.

Values:

whenDone (default)

When this is specified (or implied) the media removal occurs at
the end of any applied timing.

never

When this value is specified, the last state of the media is
kept displayed until the display area is reused (or if the
display area is already being used by another media object). Any
profile that integrates this element must define what is meant by
"display area" and further define the interaction. Intrinsic
hyperlinks (e.g., Flash, HTML) and explicit hyperlinks (e.g.,
area, a) stay active as long as the
hyperlink is displayed. If timing is re-applied to an element,
the effect of the erase=never is
cleared. For example, when an element is restarted according to
the SMIL Timing and Synchronization
module, the element is cleared immediately before it
restarts.

Used to strip the intrinsic repeat value of the underlying media
object. The interpretation of this attribute is specific to the media
type of the media object, and is only applicable to those media types
for which there is a definition of a repeat value found in the media
type format specification. Media type viewers used in SMIL
implementations should expose an interface for controlling the repeat
value of the media for this attribute to be applied. For all media
types where there is an expectation of interoperability between SMIL
implementations, there should be a formal specification of the exact
repeat value to which the mediaRepeat attribute applies. If this
attribute is defined on a SMIL layout region definition, it specifies a
default value for all content displayed within that region.

Values:

strip

Strip the intrinsic repeat value of the media object.

preserve (default)

Leave the intrinsic repeat value of the media object
intact.

As an example of how this would be used, many animated GIFs
intrinsically repeat indefinitely. The application of mediaRepeat= "strip" allows an author to remove the intrinsic
repeat behavior of an animated GIF on a per-reference basis, causing
the animation to display only once, regardless of the repeat value
embedded in the GIF.

When mediaRepeat is
used in conjunction with SMIL Timing Module attributes, this attribute
is applied first, so that the repeat behavior can then be controlled
with the SMIL Timing Module attributes such as repeatCount and repeatDur.

Used to provide author control over the sensitivity of media to user
interface selection events, such as the SMIL 2.1 activateEvent, and
hyperlink activation. If the media is sensitive at the event location,
it captures the event, and will not pass the event through to
underlying media objects. If not, it allows the event to be passed
through to any media objects lower in the display hierarchy. If this
attribute is defined on a SMIL layout region definition, it specifies a
default value for all content displayed within that region.

Values:

opaque

The media is sensitive to user interface selection events over
the entire area of the media. This is the default.

transparent

The media is not sensitive to user interface selection events
over the entire area of the media. Any user interface selection
events will be "passed through" to any underlying media.

percentage-value

The media sensitivity to user interface selection events is
dependent upon the opacity of the media at the location of the
event (the alpha channel value). If rendered media supports an
alpha channel and the opacity of the media is less than the given
percentage value at the event location, the behavior will be
transparent as specified above.
Otherwise the behavior will be as opaque. Valid values are non-negative CSS2
percentage values.

This section defines the elements and attributes that make up the SMIL
MediaOpacity Module definition. Languages implementing elements and
attributes found in the MediaOpacity module must implement all elements and
attributes defined below, as well as BasicMedia.

This attribute defines the color to be used for chroma key opacity
manipulation. It accepts a single CSS2 color value. If media objects or
implementations cannot support manipulation of the chroma key value,
this attribute is ignored. If this attribute is defined on a SMIL
layout region definition, it specifies a default value for all content
displayed within that region.

This attribute defines the opacity of the chroma key value defined
with the chromaKey
attribute. It accepts a percentage value in the range 0-100% or a
number in the range 0.0-1.0, with 100% or 1.0 meaning fully opaque. If
a chroma key color is defined, the default value is 0% (fully transparent). If no chroma key color is
defined or if implementations cannot support manipulation of the media
opacity value, this attribute is ignored. If this attribute is defined
on a SMIL layout region definition, it specifies a default value for
all content displayed within that region.

This attribute defines a color value that specifies a tolerance value
that is added and subtracted from the effective chroma key. If a chroma
key color was defined, the default value of this attribute is #000000. If no chroma key color was defined or if
implementations cannot support manipulation of the chroma key value,
this attribute is ignored. If this attribute is defined on a SMIL
layout region definition, it specifies a default value for all content
displayed within that region.

This attribute defines the opacity of the media object. It accepts a
percentage value in the range 0-100% or a number in the range 0.0-1.0,
with 100% or 1.0 meaning fully opaque. If implementations cannot
support manipulation of the media opacity value, this attribute is
ignored. The default value of this attribute is 100%. If this attribute is defined on a SMIL
layout region definition, it specifies a default value for all content
displayed within that region. The media opacity manipulation does not
apply to a background color for a media object, if such a color is
defined. The background color opacity is manipulated using the mediaBackgroundOpacity
attribute.

This attribute defines the background color opacity of the media
object for media objects that explicitly define a media background
color. It accepts a percentage value in the range 0-100% or a number in
the range 0.0-1.0, with 100% or 1.0 meaning fully opaque. If either
media objects or implementations cannot support manipulation of the
media background color opacity, this attribute is ignored. The default
value of this attribute is 100%. If this
attribute is defined on a SMIL layout region definition, it specifies a
default value for all media background opacity displayed within that
region.

This section is informative.

The attributes in this module allow the opacity (that is, the degree to
which a media object is transparent) to be defined. Opacity may be controlled
in several ways, depending on the type of media being used. For unstructured
media (that is, media that does not contain an explicitly-defined background
color), the chromaKey attribute may be used to identify a particular color
that will serve as the background color for purposes of opacity manipulation.
If a chromaKey is used, the chromaKeyOpacity attribute may specify the degree
of transparency desired. Since the color used to define a background may not
be exactly preserved within a media object, the chromaKeyTolerance attribute
allows a tolerance range to be defined for the chroma key color.

Some media objects, such as RealText, smilText, GIF, PNG, and Flash,
define an explicit background color. In these cases, the specification of the
opacity of that color can be done using the mediaBackgroundOpacity attribute.
In these cases, only the defined color is manipulated.

In addition to specifying the transparency level of a particular
background color, SMIL also allows the specification of the transparency
level of a total media object. This is accomplished using the mediaOpacity
attribute.

Note that SMIL layout also defines the backgroundOpacity attribute to
control the transparency of a layout region.

This section defines the attributes that make up the SMIL MediaClipping
Module definition. Languages implementing the attributes found in the
MediaClipping module must implement the attributes defined below, as well as
BasicMedia.

The clipBegin attribute specifies the beginning of a sub-clip of a
continuous media object as offset from the start of the media object.
This offset is measured in normal media playback time from the
beginning of the media.
Values in the clipBegin attribute have the following syntax:

The value of this attribute consists of a metric specifier, followed
by a time value whose syntax and semantics depend on the metric
specifier. The following formats are allowed:

SMPTE Timestamp

SMPTE time codes [SMPTE] may be
used for frame-level access accuracy. The metric specifier may
have the following values:

smpte

smpte-30-drop

These values indicate the use of the "SMPTE 30 drop"
format (approximately 29.97 frames per second), as defined
in the SMPTE specification (also referred to as "NTSC drop
frame"). The "frames" field in the time value may assume
the values 0 through 29. The difference between 30 and
29.97 frames per second is handled by dropping the first
two frame indices (values 00 and 01) of every minute,
except every tenth minute.

smpte-25

The "frames" field in the time specification may assume
the values 0 through 24. This corresponds to the PAL
standard as noted in [SMPTE]

The time value has the format
hours:minutes:seconds:frames.subframes. If the subframe value is
zero, it may be omitted. Subframes are measured in one-hundredths
of a frame.
Examples:clipBegin="smpte=10:12:33"

This section is informative.

The introduction of subframe notation in SMIL 2.1 introduced
an inconsistency with SMIL 1.0. As of this draft, SMIL 3.0 has
deprecated the subframe notation.

Normal Play Time

Normal Play Time expresses time in terms of SMIL clock values.
The metric specifier is "npt", and the syntax of the time value
is identical to the syntax of SMIL clock values.
Examples:clipBegin="npt=123.45s"
clipBegin="npt=12:05:35.3"

The clip begins at second 10 of the audio, and not at second 5,
since the clip-begin
attribute is ignored. A strict SMIL 1.0 implementation will start the
clip at second 5 of the audio, since the clipBegin attribute will not
be recognized by that implementation. See Changes to SMIL 1.0 Media Object
Attributes for more discussion on this topic.

The clipEnd attribute specifies the end of a sub-clip of a continuous
media object as offset from the start of the media object. This offset
is measured in normal media playback time from the beginning of the
media. It uses the same attribute value syntax as the clipBegin
attribute.
If the value of the clipEnd
attribute exceeds the duration of the media object, the value is
ignored, and the clip end is set equal to the effective end of the
media object. clipEnd may also
be expressed as clip-end for
compatibility with SMIL 1.0. Software supporting the SMIL 2.1 Language
Profile must be able to handle both clipEnd and clip-end, whereas software
supporting only the SMIL media object module only needs to support
clipEnd. If an element
contains both a clipEnd and a
clip-end attribute, then clipEnd takes precedence over clip-end. When used in conjunction
with the timing attributes from the SMIL Timing Module, this attribute
is applied before any SMIL Timing Module attributes.

This section defines the attribute extensions that make up the SMIL
MediaClipMarkers Module definition. Languages implementing elements and
attributes found in the MediaClipMarkers module must implement all elements
and attributes defined below, as well as BasicMedia and MediaClipping.

Used to define a clip using named time points in a media object,
rather than using clock values or SMPTE values. The metric specifier is
"marker", and the marker value is a IRI (see [IRI]). The IRI is relative to the src attribute, rather than to the
document root or the XML base of the SMIL document.

Example: Assume that a recorded radio transmission consists of a
sequence of songs, which are separated by announcements by a disk
jockey. The audio format supports marked time points, and the begin of
each song or announcement with number X is marked as songX or djX
respectively. To extract the first song using the "marker" metric, the
following audio media element may be used:

This section defines the elements and attributes that make up the SMIL
BrushMedia Module definition. Languages implementing elements and attributes
found in the BrushMedia module must implement all elements and attributes
defined below.

The brush element is a lightweight media object
element which allows an author to paint a solid color in place of a media
object. Attributes associated with media objects may also be applied to brush element. (A specific profile will determine the
attribute set applied to this element.)

Profiles including the BrushMedia module must provide semantics for using
a color attribute value of inherit on the brush
element. Because inherit doesn't make sense in
all contexts, the value of inherit is prohibited
on the color attribute of the brush element for profiles that do not otherwise define
these semantics.

This section defines the elements and attributes that make up the SMIL
MediaAccessibility Module definition. Languages implementing elements and
attributes found in the MediaAccessibility module must implement all elements
and attributes defined below, as well as MediaDescription.

For user agents that cannot display a particular media object, this
attribute specifies alternate text. alt may be displayed in addition
to the media, or instead of media when the user has configured the user
agent to not display the given media type.

It is strongly recommended that all media object elements have an
"alt" attribute with a brief, meaningful description. Authoring tools
should ensure that no element may be introduced into a SMIL document
without this attribute.

This attribute specifies a IRI link ([IRI]) to a long description of a media object. This description
should supplement the short description provided using the alt
attribute or the abstract attribute. When the media object has
associated hyperlinked content, this attribute should provide
information about the hyperlinked content.

This attribute specifies the position of the current element in the
order in which longdesc,
title and alt text are read aloud by
assistive devices (such as screen readers) for the current document.
User agents should ignore leading zeros. The default value is 0.

Elements that contain alt, title or longdesc attributes are read by the
assistive technology according to the following rules:

Those elements that assign a positive value to the readindex
attribute are read out first. Navigation proceeds from the element
with the lowest readindex value to the element with the highest
value. Values need not be sequential nor must they begin with any
particular value. Elements that have identical readindex values
should be read out in the order they appear in the character stream
of the document.

Those elements that assign it a value of "0" are read out in the
order they appear in the character stream of the document.

Elements in a switch statement that have test-attributes which
evaluate to "false" are not read out.

In this example, an assistive device that is presenting titles
should present the "scvad" element title first (having the lowest
readIndex value of "1"), followed by the "cardiagram" title, followed
by the "carvideo" element title, and finally present the "caraudio"
element title (having an implicit readIndex value of "0").

Note that not all examples in this specification use all media
accessibility attributes because the purpose of the sample code is to
illustrate specific language features.

This section defines the elements and attributes that make up the SMIL
MediaDescription Module definition. Languages implementing elements and
attributes found in the MediaDescription module must implement all elements
and attributes defined below.

A brief description of the content contained in the element. Unlike
alt, this attribute is
generally not displayed as alternate content to the media object. It is
typically used as a description when table of contents information is
generated from a SMIL presentation, and typically contains more
information than would be advisable to put in an alt attribute.

This attribute is deprecated in favor of using appropriate SMIL
metadata markup in RDF. For example, this attribute maps well to the
"description" attribute as defined by the Dublin Core Metadata
Initiative [DC].

The title attribute as defined
in the SMIL Structure module. It is strongly recommended that all media
object elements have a title
attribute with a brief, meaningful description. Authoring tools should
ensure that no element may be introduced into a SMIL document without
this attribute.

The SMIL MediaPanZoom module integrates the functionality of the SVG
viewBox attribute and adapts it for use within the SMIL media framework. The
SMIL panZoom attribute allows a SMIL
author to define a two-dimensional extent over the visible surface of a media
object and to subsequently project the contents within the panZoom area into
a SMIL presentation.

Most of SMIL's layout elements and attributes provide the ability to
define and manage a two-dimensional rendering space. This space is defined
relative to a root-layout (or topLayout) specification. All of the coordinate
and size specifications are in terms of the coordinate space defined for the
layout root. In contrast, the panZoom attribute allows users to define an
area in terms of the coordinate space used by the media object that is
associated with the panZoom area. The panZoom area may be smaller, equal to,
or larger than the related media object.

The following illustration shows three views of a 300x200 pixel image. In
the left view, a panZoom area is shown that is the same size as the media
object; in the middle view, a panZoom area is defined that covers the middle
part of the image only; in the right view, a panZoom area is illustrated that
is positioned (in both dimensions) partially outside the media object. Note
that while this illustration shows the panZoom area projected onto an image,
similar illustrations could be defined for videos or text objects, or any
other object that may be mapped to a particular media bounding box.

Once a portion of a media object's visible area is defined with a panZoom
area, the portion within the panZoom area is processed further as if it
defined the full native view of the media object. The content within the
panZoom area is projected into a region in a manner that is dependent on the
region element associated with that
object, including any scaling dictated by the fit attribute or (if appropriate), sub-region
positioning and alignment directives.

If the region and the panZoom area have the same aspect ratios, then the
panZoom area will, by default, fill the entire region. If the effective pixel
dimensions of the region are larger than that of the panZoom area, the effect
will be an enlargement of the media content. If the effective pixel
dimensions of the window are smaller than that of the panZoom area, the
effect will be a reduction in size of the media object. Other effects may be
obtained by manipulating the fit
attribute of the region.

If supported by the profile implementing this module, a dynamic
pan-and-zoom effect may be obtained by applying standard SMIL animation
primitives to the dimensions of the panZoom area. A pan effect may be
obtained by varying the X and Y positioning values, and a zoom effect may be
obtained by changing the size dimensions of the panZoom area. Examples of
these effects are given later in this module description. Given the nature of
independently animating collections of attribute values, care should be taken
when specifying animation behavior.

If a panZoom area extends past the viewable extents of a media object
(such as in the rightmost illustration, above), then the effective contents
of these extended areas will be transparent.

This attribute specifies a rectangular area in media coordinates that
defines the portion of a media object that is to be used within a SMIL
presentation. The panZoom attribute defines an ordered list of four
values, separated by a comma:

left

A value (using CSS2 pixel or percentage values) that defines
the minimum X coordinate of a rectangle in media space that
serves as the X origin of the panZoom area. If pixel notation is
used, the 'px' suffix may be omitted. An effective value of '0px'
represents the left edge of the media object.

top

A value (using CSS2 pixel or percentage values) that defines
the minimum Y coordinate of a rectangle in media space that
serves as the Y origin of the panZoom area. If pixel notation is
used, the 'px' suffix may be omitted. A value of '0' represents
the top edge of the media object.

width

A non-negative length value (using CSS2 pixel or non-negative
percentage values) that defines the horizontal dimension of the
panZoom area. If pixel notation is used, the 'px' suffix may be
omitted. A negative value is an error. The default value of width
is set to the intrinsic width of the associated media object.

height

A non-negative length value (using CSS2 pixel or non-negative
percentage values) that defines the vertical dimension of the
panZoom area. If pixel notation is used, the 'px' suffix may be
omitted. A negative value is an error. The default value of set
to the intrinsic height of the associated media object.

The default panZoom area behavior is to select the entire visual space
of the media object; this is equivalent to panZoom="0, 0, 100%, 100%".

The panZoom area is processed on the media object before any other SMIL
layout processing occurs. The actual visual rendering of the content
resulting from the processed panZoom area will be determined by, among other
factors: the size of the target region, the application of sub-region
positioning in that region (if supported by the profile), the value of the
fit attribute on the region, and the effect of SMIL alignment attributes (if
supported by the profile).

This section is informative.

If the profile integrating the panZoom element allows each of the
attribute values to be animated, care should be taken to choose an animation
calculation mode that will yield predictable results (such as using a linear
mode). The animation of mixed percentage/pixel values for height and width is
not recommended.

Note that the specification of negative values for left and top is not an
error; this allows placing (a portion of) the panZoom area outside of the
media.

This attribute is identical in definition to the panZoom attribute defined for the
ref element in this section, with the exception that it defines a
default panZoom area that is applied to all media rendered in the
associated region. All other aspects of panZoom area processing are the
same as with the ref element, except that the values defined for the
panZoom area on a region may be overridden by a panZoom area
specification on the ref element.

In this example, a single region is defined that is used to display four
instances of the same image. Each media reference within the sequence S
contains a different panZoom area definition, each of which will result in
the following behavior:

The media reference R1 defines a panZoom area that encompasses the
entire media object space; the full image will be shown in region I, as
is shown in the following image:
Note that the origin of the image is aligned with the origin of the media
object, at the top-left of the region.

The media reference R2 defines a panZoom area that encompasses the
center portion of the media object space. The projection of the media
into region I will result in a zoom into the source image, as is shown in
the following image:

Note that the origin of the sub-image defined by the panZoom area is
placed at the origin of the top-left of the region. Note also that the
value of the fit attribute determines that the image is scaled (while
maintaining the aspect ratio), resulting in the zoom effect.

The media reference R3 defines a panZoom area that is the same as in
reference R2; the difference in this example is that the value of the fit
attribute does not permit enlargement of the source image into the
region. As a result, the image is placed at top-left in an unscaled
rendering:

The media reference R4 defines a panZoom area that extends beyond the
boundaries of the media object. When it is projected into the region I
with a fit value that scales the image with preserved aspect ratio, the
entire extent of the panZoom area is scaled: the areas that extend beyond
the image content are rendered as (scaled) transparent content:

All of the previous examples illustrate how a panZoom area operates on a
media object that contains a media-defined viewable extent. The panZoom
attribute may also be applied to visual objects that do not have predefined
extents. Consider the following example, in which an unstructured text object
is placed in a region:

In this example, a single region is defined that is used to display a
undimensioned text object. In SMIL 3.0, the text object would first be
rendered to an off-screen bitmap based on the default settings for the media
object (font, font size, font color) and then a panZoom area of the defined
size would be overlaid on this text representation. This facility is
especially useful when combined with SMIL Animation, as discussed in the next
example.

The ability to define a panZoom area, when combined with SMIL animation
primitives, provides a simple mechanism for doing pan/zoom animations over a
visual object. (These pan/zoom animations are often called 'Ken Burns'
animations.) The following example illustrates how a pan window may be
positioned and moved over an image area:

In this example, an image with intrinsic size of 233x150 pixels is
rendered into a region of size 50x75. An initial panZoom area is defined that
displays a 50x75 portion of that image, positioned in its top-left corner.
During the following 20 seconds, the panZoom area is moved across the image
according to the behavior of the animate element; the panZoom area changes
are scheduled at equal points across the animation timeline (in this case,
every 5 seconds). During the final animation, the panZoom area is extended to
implement a zoom-out across the entire image. An illustration of the
rendering results is shown below:

The MediaPanZoom module allows individual media object references to
override the default values for certain attributes. In all cases, the
attributes will apply only to the (sub-)region referenced by the media
object. Changes will not propagate to child sub-regions or to parent
regions.

The functionality in this module builds on the viewBox definition of SVG.
Unlike SVG, the SMIL panZoom attribute defines a logical sub-image that
contains only content within the panZoom area; SVG uses the viewBox to define
a minimum viewing dimension for content, but allowing content outside the
viewBox to be displayed in the region.

The MediaPanZoom module does not define a preserveAspectRatio attribute,
since this functionality is already provided by the SMIL fit and
registration/alignment attributes.

Using attribute names with hyphens such as clip-begin and clip-end is problematic when using a
scripting language and the DOM to manipulate these attributes. Therefore,
this specification adds the attribute names clipBegin and clipEnd as an equivalent alternative to
the SMIL 1.0 clip-begin and clip-end attributes. The attribute names
with hyphens are deprecated.

Authors may use two approaches for writing SMIL 3.0 presentations that use
the new clipping syntax and functionality ("marker", default metric) defined
in this specification, but can still can be handled by SMIL 1.0 software.
First, authors may use non-hyphenated versions of the new attributes that use
the new functionality, and add SMIL 1.0 conformant clipping attributes later
in the text.

SMIL 1.0 players implementing the recommended extensibility rules of SMIL
1.0 [SMIL10] will ignore the clip attributes
using the new functionality, since they are not part of SMIL 1.0. SMIL 3.0
players, in contrast, will ignore the clip attributes using SMIL 1.0 syntax,
because the SMIL 3.0 syntax takes precedence over the SMIL 1.0 syntax.

The second approach is to use the following steps:

Add a "system-required" test attribute to media object elements using
the new functionality. The value of the "system-required" attribute would
correspond to a namespace prefix whose namespace IR ([IRI]) points to a SMIL specification which
integrates the new functionality.

Add an alternative version of the media object element that conforms to
SMIL 1.0